Vibration dosimeter worn by an operator

ABSTRACT

A vibration monitor is provided which is worn on the wrist of an operative for an operating plant or apparatus. The monitor includes a piezoelectric transducer and associated circuitry which generates electronic digital signals during the periods when vibrations are experienced by the operative. Preferably, the plant or apparatus has a transmitter which transmits a code identifying the plant which is received by the monitor. Alternatively, the code may be entered manually. The monitor preferably includes a logger which can be connected to a host computer which data can be transferred over an external communications link. The logger includes a storage device for storing how long the operative is subjected to vibrations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to vibration monitors.

2. Related Art

Personnel are required to operate in the field of gas operationsapparatus such as road breakers, vibro tampers, rock drills, poletampers and hand drills for example all of which impose vibrations onthe hands of the operator. In other fields, operatives are required touse similar or other vibratory apparatus which impose vibrations on thehands or on other parts of the body or on the body as a whole. Thesevibrations can cause disease.

SUMMARY OF THE INVENTION

The invention is concerned with providing a low cost vibration monitoruseful in monitoring the vibrations experienced by an operative.

According to the invention there is provided a vibration monitor to beworn by an operative comprising:

means for identifying plant or equipment in use by the operative toallow a predetermined vibration level value associated with that plantor equipment to be available to the monitor;

sensor means for detecting that vibration is occurring; and means fordetermining the elapsed time during which the vibrations are detected.

A code identifying the apparatus responsible for imposing the vibrationscan, in one form of monitor, be manually entered into the monitor;alternatively the code can be transmitted by a transmitter attached tothe plant and received by the monitor.

Alternatively, the actual value of the previously-measured vibrationmagnitude of the apparatus responsible for imposing the vibrations istransmitted by a transmitter attached to the plant and is received bythe vibration monitor as the expected vibration level.

Preferably, the data logger has an external communication facility whichallows communication with a visual display, printer, computer, or otherdata processing device.

Further according to the invention there is provided a method ofmonitoring vibration imposed by apparatus on an operative andcomprising:

idenitifying plant or equipment in use by the operative to allowpredetermined vibration level value associated with that plant orequipment to be available to the monitor;

sensing whenever vibrations are occurring and determining the elapsedtime during which the vibrations are detected.

The data captured may be processed to give an accumulated measure of thevibration dose experienced by the operative.

Still further according to the invention there is provided a plantidentity mechanism for use with a vibration monitor including means forproducing an output indicative of the plant or equipment being utilisedto allow vibration levels to be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of vibration monitor and associated equipment willnow be described by way of example with reference to the accompanyingdrawings in which:

FIG. 1 is a block diagram of a basic vibration monitor;

FIG. 2 is a block diagram showing the principal components of vibrationmonitor;

FIG. 3 is a block diagram showing a personal vibration monitor;

FIG. 4 is a block diagram of an automatic plant recognition transmitterusing a piezo electric kinetic power source;

FIG. 5 is a block diagram showing the main elements of a logger usedwith the vibration monitor;

FIG. 6 shows a flow chart associated with the FIG. 5 operation; and

FIG. 7 is a block diagram of a vibration monitor showing a host computerto which it is connected.

THE ARRANGEMENT OF FIG. 1 SHOWS AN IMPLEMENTATION OF A BASIC VIBRATIONMONITOR.

Vibrating plant or apparatus is shown at 10 imposing vibrations on auser or operative (shown schematically as block 12). The operative wearsthe vibration monitor 14, preferably on his wrist though other locationsare possible.

The vibration monitor 14 could emit an alarm when the accumulatedvibration dose exceeds a predetermined threshold, although it canalternatively simply record the time period over which the vibrationsare detected.

In order to reduce the cost of the device, the monitor is designedsimply to determine that vibrations are occurring and not to measure theactual level of the vibrations. The expected level of vibrations isknown for any given apparatus to be used by an operative, because thesewill have been premeasured when designing the system and valuesprestored within the monitor. This information can then be identifiedfor any given apparatus or plant which is to be used.

A code identifying the type of apparatus 10 is manually entered into thevibration monitor 14. For example, a set of keys (not shown) fitted tothe monitor 14 may be operated by the operative 12 which result in theinsertion of the code. The code identifies the type of apparatus andhence the level of vibration expected when it is used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As the vibration monitor requires a low cost vibration measurementtransducer and the most commonly used and economical transducer forvibration is the accelerometer (typical cost £50) this is too expensivewhen compared to the target cost of the monitor. It became clear that analternative to commercially available vibration transducers wasrequired. Following experimentation, it was discovered that a piezoelectric sounder disc could be used in conjunction with suitable signalprocessing electronics to fulfil the need.

Piezo electric sounder discs are generally thin circular discs, with twoelectrodes, and are available in diameters suitable for incorporation inthe monitor described so far. These discs are commonly used as audiosounders in, for example, digital wrist watches which cost only a fewpence.

FIG. 2 shows a schematic diagram of the piezo-electric transducer andthe associated electronic circuitry used in the vibration monitor whichis used merely to determine that vibrations are occurring rather thanmeasuring the specific value or level of vibration.

The monitor would typically be of the approximate size and shape of awrist watch, and would be worn as such.

The piezo-electric transducer 20 is subjected to an acceleration, e.g.as produced by vibrations from the vibrating apparatus 10 and a verysmall voltage is generated. This voltage is amplified in amplifier 22and passes through filter 24. The voltage Vs after the filter 24 iscompared with a reference voltage Vr from a voltage source 26 in acomparator 28. If Vs is greater than Vr then a change in state occurs ina binary switching signal provided at output 30. If Vs is less than Vrthen the digital output signal reverts to its previous state. Hence asimple vibration detector is provided which provides a signal indicativethat vibrations are occurring above a predetermined threshold withoutthe need to actually measure the value itself.

FIG. 3 shows a personal vibration monitor in a preferred form whichincludes a wireless receiver 30 to receive information concerning theplant 10 being utilised.

The apparatus or plant 10 has firmly fitted to it a low frequencytransmitter 31 which transmits a coded burst of data periodically to themonitor so that it can determine the type of apparatus being utilisedand hence the levels of vibrations which will be experienced.Information on the types of equipments and the usage is stored in logger32. Different types of equipment may be used by an operative in any oneday and the cumulative levels can be stored.

FIG. 4 shows one form of automatic plant (or apparatus) recognition(APR) transmitter system 31 powered by a kinetic electrical generator.

The transmitter power source, typically piezo electric generator 40utilises the kinetic energy of the plant when in use, to provideelectrical power by converting the mechanical energy to electricalenergy. The output is rectified, filtered and regulated by circuit 41 toprovide a suitable electrical output, capable of operating thetransmitter and associated control electronics. Such a permanent powersource eliminates the need to replace batteries, etc. for maintenance ofthe transmitter.

A vibration detector 42 similar to that of the monitor is employed todetect when the plant is actually being operated. This signal isreceived by controller 43 so as to only send signals to the monitor whenthe apparatus is in use via the data encoder 44 and transmitter 45. Thepower is sufficiently low so that the signal is only received by theoperator actually using the plant transmitting the code identifying theplant.

In an alternative form, the APR system may be powered by a batterysupply or a solar cell/rechargeable battery combination.

This data transmitted provides information about the plant. Eachtransmitter may be programmed with a code, which uniquely identifies theplant type to which it is fitted. This allows many types of plant to beused with the vibration monitor.

The transmitter only sends its coded data, when the plant is in use,otherwise it is quiescent.

The logger 32 within the monitor of FIG. 3, which converts the receiveddata burst from receiver 14, back to plant identity information. Thedata transmitted from the plant includes error checking, which providesa measure of security against incorrect plant information being logged.In use, it is conceivable that there may be several users, who areequipped with vibration monitors therefore the logger will only recordplant information, when it experiences valid vibration trigger events.This together with the use of the low power (therefore short range)transmitter, largely precludes other users from acquiring plantinformation when not appropriate. This approach allows the receiverwithin the logger to be deactivated during periods when there are novalid vibration trigger events. This allows a power saving, and thus anincrease in service life between battery changes in the logger.

In order to collect the information necessary, to allow an individuals'vibration exposure to be calculated, a recording system, employing anelectronically re-writable memory was designed for the logger and isshown in FIG. 5. The approach chosen allows several tasks to be carriedout by the same electronic system. The logger must carry out thefollowing operations:

(1) Record the type of apparatus responsible for the vibration, providedthat such apparatus are catered for;

(2) Be able to time and date ‘tag’ valid records;

(3) Record the duration of any valid vibration event;

(4) Determine the validity of a vibration event for an exposurecalculation; and

(5) Be able to communicate the stored information to a system which can,by using this information together with information relating to thevibrating apparatus, allow an individuals' vibration exposure to becalculated.

The vibration monitor described so far is intended to be ofapproximately the same size and shape as a wrist watch. In consideringthe above requirements, it is clear that any power source to beintegrated within the above package and run the electronics must besmall and therefore will have limited capacity. To this end low power,low voltage electronic devices are used in FIG. 5.

The main controller (A) logging operations is an 8 bit low voltage/powermicrocontroller, e.g. Phillips chip type P85CL00HFZ.

An audible warning device (B) is connected to the controller as is avisual warning device (C).

The accelerometer and signal processing electronics (D) has already beendescribed above in FIG. 2.

The apparatus or plant recognition circuit (E) is shown which receivesplant ID information for the controller.

A battery condition monitor (F) measured battery condition and caneffect shutdown.

A real time clock and logger configuration data store (G) providestiming and operation data.

An 8 kilobyte logged data store, e.g. EEPROM provides informationstorage.

A serial (RS423) 3 wire communications link (I) provides the path forincoming and outgoing data (typically using an external host computer).

A flow chart suitable for monitor system operation is shown in FIG. 6.

The monitor arrangement linked to a host computer is shown in FIG. 7.The block I of FIG. 5 is linked to the communications interface 50 tothe host computer 51. Information to be printed out is available viaprinter 52.

Functional Description of Logger

Quiescent Mode

While not logging a valid vibration event, the logger will attempt toconserve power. In practice, this will mean that the device electronicswill power down, with only the battery monitor, plant recognition andaccelerometer circuits being active. These are necessary features, whichpermit the user to be notified of a low battery condition, as well asproviding the means whereby vibration can be monitored continuously,forcing data to be logged only under valid conditions.

Alarm Mode

Valid alarm conditions are:

Logged data exceeds 95% of the memory capacity (inactive when in standbymode)

Low battery warning

Invalid plant identity received (inactive when in standby mode)

Communications error

Internal fault detected

When an alarm condition is detected the logger will sound and indicatean alarm. Such indications may be periodic. During the intervening timethe logger will enter the quiescent mode described above. The onlymethod of cancelling alarms will be via the host computer system, whichwill record the type, time and date of the latest alarm.

Standby Mode

The logging of data is disabled, and the logger is in the quiescentmode. The host computer sets standby mode.

Clear Mode

This is a transient condition, set by the host computer, alwaysterminating in the standby mode. The following operations are carriedout:

Logged records counters are reset to 0

Alarms and related logger data are cleared

The current plant identity is reset to the default value

If modem based communications are implemented, the blacklisting count isreset to 0 (only allowed in the local communications mode).

Although it is preferred that the identification of apparatus be doneautomatically, it is possible in an alternative to manually enter theidentification code. A set of keys, which may be colour coded, are usedto enter a code which uniquely identifies a plant type. The use of thekeys will signal a wake-up condition to the logger microcontroller. Thelogger will leave the quiescent mode.

This method of entering plant information could lead to errors if theoperator unwittingly enters inappropriate information relating to thewrong type of equipment.

The vibration monitor shown in FIG. 3 could be used as a monitor, ratherlike a radiation badge, the user's exposure being constantly monitored.If the total cumulative exposure exceeds a present value the user issignalled via an audio and/or visual indicator, e.g. flashing light orbeeps. The exposure level at which this signal occurs would be eitherprogrammed via a communications link with the host computer or may bepreset at manufacture.

The dosemeter as shown above, would have plant data stored internally inthe form of a look-up table. Associating the plant data, together withthe exposure duration, allows the daily exposure level to becontinuously monitored. The monitor could also calculate the cumulativedose over a period of time set alarm thresholds programmed for variouscumulative exposure levels.

The monitor may also include a digital display which would show thedaily exposure and the cumulative dose over several days.

Logging Mode

The logging mode is normally entered subsequent to the quiescent mode.Logging of an elapsed time record begins upon receipt of a valid triggercondition.

Trigger information is provided by a digital pulse applied to one of themicrocontroller input pins. This signal occurs whenever the inputtransducer experiences an acceleration typically more than 3ms⁻². Whilea valid trigger exists an internal counter measures elapsed time. Whenthe valid trigger conditions are no longer true the record start time,date, source and elapsed time are written to the logger's non-volatilememory. The logger then re-enters the quiescent mode.

NOTE: Following the first occurrence of a valid trigger the current dateand time is written to the logger's working memory.

External Communications (with host computer—see FIG. 7)

The communication link with the host PC allows the logger to beconfigured as well as enabling data held in memory to be down-loaded tothe host for post processing. Logging may continue during a dialogue,however, there are some restrictions to this (see below). This featureprovides the following advantages:

1. The logger data can be monitored in real time.

2. The logger may be used as a remote instrument.

3. The calibration accuracy of the logger can be checked.

4. Provides a powerful debugging tool during instrument development.

5. The external communications facility may include support formodem-based remote communication. This is an optional facility.

The vibration monitor shown in FIG. 3 contains a semiconductor memorywhere the exposure duration, together with the type of plantresponsible, is stored. Plant or apparatus details may be storedinternally in the meter in the form of a look-up table or may be held ina host computer memory.

The logger will include facilities to communicate with a computer whichwill allow:

1. The download of logged data.

2. Setting of exposure level thresholds (if applicable).

3. Updating plant related details (when stored internally).

4. Other operations associated with the logging of vibration exposures.

The instrument may also incorporate any or all of the featurespreviously described.

This configuration allows a workforce equipped with vibration loggers tobe managed in respect of their plant usage and overall exposure tovibration. Analysis of each users exposure record being carried out by ahost computer system.

The vibration monitor 14 shown in FIG. 3 may include a digital displayshowing vibration exposure level.

To re-cap, the vibration monitor may be implemented in several differentways:

1. PERSONAL MONITOR

A monitor, containing a look-up table of plant or apparatus type, crossreferenced with weighted acceleration factor for each type of plantcatered for. This will allow the current vibration exposure level to becalculated by the dosemeter itself.

2. VIBRATION LOGGER

A monitor which logs vibration exposure time, together with type ofplant or apparatus responsible for each exposure record. The actualexposure level being calculated following the transfer of logged data toa host or base station computer.

3. PERSONNEL MONITOR AND LOGGER

A monitor which incorporates all the above features.

A system in which monitor data can be transferred to a host or basestation computer will allow both analysis and management of a user'svibration exposure. Potentially, the host or base station computersystem could be used to analyse data for many monitor users.

What is claimed is:
 1. A vibration monitor to be worn by an operativecomprising: means for identifying plant or equipment in use by theoperative to allow a predetermined vibration level associated with thatplant or equipment to be available to the monitor, said identifyingmeans receiving an identifying code identifying the plant or equipmentin use from a transmitter, including a kinetic power source, associatedwith the plant or equipment in use; a piezoelectric sensor for detectingthat vibration is occurring, and means for determining the elapsed timeduring which vibration is detected.
 2. A monitor as claimed in claim 1wherein the means for identifying equipment includes means for receivinga code indicative of the equipment to be utilized or the level ofvibration to be expected.
 3. A monitor according to claim 1 in which acode identifying the apparatus responsible for imposing the vibrationscan be manually entered into the vibration monitor.
 4. A monitoraccording to claim 1 in which a code identifying the apparatusresponsible for imposing the vibrations is transmitted by a transmitterattached to the vibrating equipment for receipt by the vibrationmonitor.
 5. A monitor according to claim 4 wherein the transmitterincludes a kinetic power source.
 6. A monitor according to claim 1wherein storage means are provided for recording accumulated durationinformation and access means are provided to allow the accumulatedduration information to be made available externally of the monitor. 7.A monitor as claimed in claim 6 wherein the information is madeavailable by means of a computerized communications link.
 8. A monitoraccording to claim 6 wherein the storage means includes means foridentifying the date and time of day to accompany the accumulatedduration information.
 9. A monitor according to claim 1 wherein thevibration sensor is a binary device for producing a first signal whenvibration is detected and a second signal when no vibration is detected.10. A monitor as claimed in claim 1 wherein a calculator means isprovided for producing an indication of total accumulated time anddegree of vibration over a given period.
 11. A monitor according toclaim 1 wherein alarm means are provided to indicate when accumulatedexposure reaches a predetermined level.
 12. A method of monitoringvibration imposed by apparatus on an operative and comprising:identifying plant or equipment in use by the operative to allow apredetermined vibration level associated with that plant or equipment tobe available to a monitor by receiving an identifying code identifyingthe plant or equipment in use from a transmitter, including a kineticpower source, associated with the plant or equipment in use; andsensing, using a piezoelectric sensor, whenever vibrations are occurringand determining the elapsed time during which vibrations are detected.13. A method as claimed in claim 12 including the step of storingvibration information concerning equipment to be utilized so as todetermine accumulated vibration exposure for a given time.
 14. A methodas claimed in claim 12 including transmitting coded information from theutilised equipment by wireless means to identify the equipment beingoperated.
 15. A method as claimed in claim 13 wherein information fromthe utilized equipment is communicated to a remote computer via acommunications link.
 16. A plant vibration monitoring system comprisinga plant identity mechanism including means, carried by a plant orequipment being used, for producing an output indicative of the plant orequipment being used and a vibration monitor adapted to worn by anoperative and including identifying means for sensing said output so asto identify the corresponding plant or equipment being used so as toallow a predetermined vibration level value associated with thecorresponding plant or equipment to available to the monitor; detectingmeans, including a piezoelectric sensor, for detecting that vibration isoccurring and for determining the elapsed time during which vibration isdetected, said plant identity mechanism comprising a transmitter,including a kinetic power source, associated with the plant or equipmentin use, for transmitting an identifying code identifying the plant orequipment in use.
 17. A mechanism as claimed in claim 16 wherein themeans includes a transmitter attached to the plant for transmitting acode indicative of the type of equipment being utilized.
 18. A mechanismas claimed in claim 17 wherein the means includes a transmitter attachedto the plant for transmitting information indicative of the level ofvibration expected for that equipment.